In the production of steel, it is common practice to perform distinct process steps either in the same vessel or to perform a first portion of the process in one vessel and second portion in a separate vessel. For example, it is common in the use of electric arc furnaces for the processing of steel to employ separate slags for oxidation and refining. Initially, a melt down period is provided to form a molten bath. During oxidation, silicon, manganese, carbon and other materials in the melt are oxidized. The oxygen for this purpose may be provided in a number of ways, such as by an oxygen lance, the furnace atmosphere, the calcination of limestone or oxides from alloying elements and/or ores which may be added to the furnace charge. During the oxidation period, the melt is covered by an oxidizing slag which typically includes large percentages of oxides of iron, aluminum, magnesium, manganese and phosphorous. At the end of the oxidizing period, it is generally the practice to deslag the melt by cutting off the power to the electrodes which are then raised, tilting the furnace and racking off the oxidizing slag through a slag door. The furnace would then be charged with materials such as burnt lime, fluorspar, silicon, sand and powdered coke to form a reducing slag which would be maintained during the reducing period. The disadvantages of the multi-slag electric arc furnace steel making process is that it is relatively lengthy and results in a high iron loss as the result of the deslagging operation.
It is a common practice in electric arc steel making to preheat scrap before charging so as to reduce the duration of the meltdown period. This has not been wholly satisfactory because it involves additional handling and equipment.
There are also a number of metallurgical vessels presently employed which perform an inactive function, such as metal storage or are limited in the functions that can be performed, such as induction melting furnaces.